One of the world's prime symbols of natural heritage and its history of research, known under the vernacular name "human fish" or the olm, Proteus anguinus, is a blind amphibian strictly endemic to the subterranean waters of Dinaric karst. It is the only European cave vertebrate, and the largest cave animal in the world.

Proteus is a globally threatened species. Although the IUCN Red List of Threatened Species defines it as vulnerable, and it is a priority species under both the Bern Convention (Appendix II) and the EU Habitats Directive (Annex II* and IV), no monitoring scheme for Proteus exists. Due to its high specialization to a narrow range of abiotic conditions in the subterranean environment, Proteus (and other groundwater organisms) is extremely vulnerable to direct and indirect alterations of its habitat. Recent negative human influences come from intensive agriculture, energy production, and unregulated urbanization. In Bosnia and Herzegovina these are reaching catastrophic proportions.